Dead tach - filter?

by Fishgrinder Fri Dec 06, 2013 6:34 am

The factory tachometer in my 1975 Monte Carlo is dead..almost. The circuit board should be ok, in fact I got a burnt circuit repaired this summer. Before that the needle was frozen at 2000rpm all the time. But after the repair it drops down to 0 once I turn the ignition on. So now it receives power. The wire that comes out of the firewall is hooked to the Tach terminal on the HEI.

I've read that many cars had tachometer filters to smooth out the HEI-pulses, and that a malfunctioning one would cause a dead tach.

Does anyone know if our cars came with these, where were they located?

by 77mali Fri Dec 06, 2013 8:28 am

This guy might be able to answer that. He can also repair your tach right if you want- see the very bottom of this web page.

http://www.tachman.com/gm.htm

by Mcarlo77 Sat Dec 07, 2013 3:52 pm

Here's a pic of what I believe is an inline filter (that round thing). I pulled this off a '75 Laguna with factory tach. This is the wire that passes through the firewall and to the distributor. Unfortunately, someone beat me to the tach cluster.

Dead tach - filter? Tachga10

Don't mean to hijack this thread, but I've also got a question regarding tachs on these cars. When I removed the gauge cluster from the parted out '76 Laguna, someone had placed a tach in place of the Economy Gauge. It wasn't hooked up and was for looks only, I guess. Anyway, was going to install this gauge cluster in my '75 Laguna as it just came with warning light cluster (I've got all the underdash/underhood wiring for the gauge setup from the above mentioned '75 Laguna). Here's my confusion...the connecting pins on the back of the tach do not mate up with the electrical plugs in the gauge cluster housing. They sit too low in relation to the plugs. I've confirmed via part number stamped on the back of the tach that it is from a '73/'74 Chevelle...if that makes any difference. I've also seen the back of a '73 or maybe '74 tach gauge cluster (has the AMP gauge instead of VOLTS) and those plugs sit higher on the housing, too. What am I missing? Could the '73 tach/housing pin location be unique to that one year? Doesn't seem likely as the parts book only shows one flex circuit for '73 & '74 Chevelles with gauges...and, that would indicate to me the proximity to the plug location on the housing would be the same. Do I just use jumper wires to make the connections and move on with life? Fishgrinder...if you happen to remove your tach again, please take a pic of the back connecting pins for comparison.

Back of my Tach:

Dead tach - filter? Tachga11

Back of '73 or '74 (not positive which) Tach Gauge Cluster w/AMP Gauge:

Dead tach - filter? 73or7410

by 77mali Sat Dec 07, 2013 4:37 pm

73 had voltmeter, was the only year & the circuit board is unique also. Some 73's also had a set up for wiring the tach to the right of the gas pedal on the firewall. The Tachman link that I posted shows an "electronic refurbish" of the G-3 Tach. It will run independently of the board with the upgrade I believe so it won't matter if the pin's don't match. I talked to the guy to see if he hand any that were already done a couple of years ago. He doesn't keep them on the shelf but I think it was only like a $90 or $100 job at the time.

Another option is a new C/B for 73 which are avail aftermarket from OPG & others. They are pretty easy to remove the only tricky part are the metal tabs holding them in to the gauge housing.

by Fishgrinder Sat Dec 07, 2013 4:39 pm

That's a great picture Mcarlo77! Just to double check: the long side of the wire and the filter is inside the car?

I will take a picture of the tach if I pull it again, but I doubt it will happen if the filter is the sole reason for the defect, and unfortunately not until the spring.

by Mcarlo77 Sat Dec 07, 2013 8:39 pm

"73 had voltmeter, was the only year & the circuit board is unique also".

Wait...you mean '73 was the only year for the AMP gauge, right? I've heard that too... but if it's true, why does GM show the same circuit board part number for both '73 & '74 with gauges (#8908200)? Plus, the part number on the back of the tach also correlates with GM's part number for a '73/'74 (#5657612). You can Google these part numbers and there are a couple links to GM parts manuals showing which years they apply to. Also, here is a pic I took of a tach gauge package in a '74 Chevelle brought here from CA with AMP gauge (I'm still the proud owner of the rust-free doors from this car...ha!). Hard to read, but I can enlarge the photo on my computer and it definitely says "AMPS". I'm confused...

Dead tach - filter? Pair7410

by Mcarlo77 Sat Dec 07, 2013 8:46 pm

[quote="Fishgrinder"]That's a great picture Mcarlo77! Just to double check: the long side of the wire and the filter is inside the car?

If I remember correctly, the filter was bolted to the outside firewall...hence the rust on it.

by 77mali Sat Dec 07, 2013 9:41 pm

Manufacturing date code note 1973
Dead tach - filter? P1050710

74

This is my 75 Tach backside- IDK for sure but I think you have a 73 tach there?
Dead tach - filter? P1050712

The font is different on 73 clusters they came w/ 120 mph speedo vs 75/76 versions w/ 100 mph speedos....I'm not 100% sure of 74 but I think the font is the same as 73 w/ 120 mph speedo & volt vs amp meter (your correct there) 73 was AMPS, my bad...winter brain syndrome.

The 73 C/B for tach set up looks like this. I got this set up from a reputable member here last year. My tach does not exactly correspond with the "prongs" in the 73 gauge pod so I'm not sure how to cure that (except maybe sell/swap my set for a set of 73's or swap over the 74 c/b & slightly modify the back of the 73 gauge pod to fit- I haven;t had a chance to figure it out this season). My gauges are from 75 even though the c/b was made in 74.

Dead tach - filter? P1050713

by Mcarlo77 Sat Dec 07, 2013 10:26 pm

Paul...wouldn't that date code of U82374 possibly be about the time they'd be changing over to the '75 model year cars? And likewise, the S111373 would be for the '74 model year? What are the GM part numbers on the opposite end of the c/b's? I'm guessing 8986113 for the U82374 and 8908200 for the other one?

by 1973 454 MONTE Sun Dec 08, 2013 11:47 am

ok,at the moment i have 3 clusters.
Dead tach - filter? All310

early 73 tachs had a "5" on them. (this is with bucket speedo)
Dead tach - filter? Early710

early 73 tach with a bench speedo
Dead tach - filter? Late7310

this tach is late 73 and all 74s (but this is out of a 73 bucket seat car)
Dead tach - filter? 7410

by 77mali Sun Dec 08, 2013 12:38 pm

Mcarlo77 wrote:Paul...wouldn't that date code of U82374 possibly be about the time they'd be changing over to the '75 model year cars? And likewise, the S111373 would be for the '74 model year? What are the GM part numbers on the opposite end of the c/b's? I'm guessing 8986113 for the U82374 and 8908200 for the other one?

Yes, the 75 set up is 8986113, the 73 is 8908200. I just put the 75 c/b over the 73 (which is installed on the gauge pod) & the only difference is that there is one extra pin that goes to the amp gauge on the 75.
Dead tach - filter? P1050716

I also test fitted my tach and it fits in the pod with all the 73 stuff- NO ISSUES with the prongs not lining up! It's been so long since I worked on anything other than a motor that I'm starting to forget all the stuff I did before hand. Sorry if I confused or confounded you.

Why the h3ll do the back our our tach's look so different? Are you missing the circuit piece?

by 77mali Sun Dec 08, 2013 12:55 pm

Also that link you posted for Fish- I have that set up less the cord to the tach itself installed on my fuse box-
Dead tach - filter? P1030110

Maybe the previous owner had a tach hooked up at one time? Somewhere I have the rest of it that I got with the 73 gauge pod from Bigredlaguna...wish I could find it, LOL

by Mcarlo77 Sun Dec 08, 2013 1:28 pm

I just noticed a date code on the back of the tach...2273 (mid-model year '73). I, too, wonder why I don't have an exposed circuit board on the back. Mine must be inside that protective case? Can't remove it to look as it's riveted to the tach face plate.

Another question is why your tach has 6 pins on back. I'm guessing it's the upper three that engaged with the housing plugs?

And Chris...are you confirming the plug position on the housing for the tach pins are the same whether '73 or '74? If so, that would confirm GM's one part number for the flex circuit (w/gauges) for both years. If all this is true, why does my tach only have three pins and they all sit too low to mate with the plugs? WTF?!!

by Mcarlo77 Sun Dec 08, 2013 1:31 pm

No, Paul...that cylinder mtd on the fuse box is a different kind of resistor/capacitor or whatnot. They all have that.

by 77mali Sun Dec 08, 2013 1:45 pm

Mcarlo77 wrote:No, Paul...that cylinder mtd on the fuse box is a different kind of resistor/capacitor or whatnot. They all have that.

Damit! What the heck is it for then?

The three upper pins do engage the prongs on the cluster housing. IDK what the extras are for either. Maybe Chris can confirm if the 73 should have the exposed board or not. Tachmans web page shows a tach similar to mine and says that it was GM's first attempt at an "air coil" movement for it's tach's (whatever that is).

by Mcarlo77 Sun Dec 08, 2013 2:04 pm

It came that way from the '76 Laguna I parted out. As I mentioned, it wasn't hooked up in that car. Does your tach have that metal casing like on mine underneath the circuit board? Suppose I've got nothing more than a friggin' paperweight...

by 77mali Sun Dec 08, 2013 2:14 pm

Here is a pic of mine in the same position you had posted.
Dead tach - filter? P1050717

Worse comes to worse Gary the Tachman can put one on for you.

by Mcarlo77 Sun Dec 08, 2013 5:06 pm

Visited "The Tachman" website and, lo and behold, he shows the same tach as I've got...part number and all. It appears I am missing the circuit board that would have the three upper pins that would connect to the housing plugs. Guess I'll have to contact him and see what that's going to cost. Anyone have any experience with this guy?

FISHGRINDER: After spending much time reading up on tach filters, it would sure seem to me that is your problem. Numerous threads of guys who's tachs suddenly quit working...and, a new filter fixed it. Many didn't have a filter in place to begin with and their tachs worked fairly well until one day it would just quit working. None, however, revealed where they bought the filter; except to say "online". From reading these, I got the impression GM used the same basic filter setup for most mid-70's thru 80's cars with HEI. Let us know what you find out.

by Fishgrinder Sun Dec 08, 2013 5:29 pm

Thanks Mcarlo77 and 77mali.

I looked under the hood and couldn't find the filter housing there. There's only a short stump of wire coming out of the firewall, just enough to reach the distributor. But I do have a similar setup in the fuse box, like in your picture 77mali. I'll have a closer look one of these days.

by Mcarlo77 Sun Dec 08, 2013 5:36 pm

"Guess I'll have to contact him and see what that's going to cost.

YIKES...just saw on website where he's charging $250 to refurb a tach! Sumbitch!!!

by 77mali Sun Dec 08, 2013 5:52 pm

Steve give him a call, he's a good guy & knows his $h!t. I think that $250 is for a complete restoration & not the electronics upgrade. I could be wrong but I seem to remember it was about $100 or so.

by 1973 454 MONTE Sun Dec 08, 2013 5:55 pm

steve
i will go out tomorrow and get some more pics for you

by 77mali Sun Dec 08, 2013 6:50 pm

Fishgrinder wrote:Thanks Mcarlo77 and 77mali.

I looked under the hood and couldn't find the filter housing there. There's only a short stump of wire coming out of the firewall, just enough to reach the distributor. But I do have a similar setup in the fuse box, like in your picture 77mali. I'll have a closer look one of these days.

Thanks for the thread hijack, lol. Turned into one of the best discussions about stock tachs & gauges in a good while.

by Mcarlo77 Fri Dec 13, 2013 3:30 pm

Hey, Fishgrinder...any luck contacting Gary the Tachman? It's been three days now for me and, after a couple attempts to call him and an e-mail, no word from him. Not exactly exemplary customer service IMO.

However, in an amazing stroke of luck, I actually located probably one of the last NOS '75 tachs left on the planet...and, it was right in my backyard! Small, one-man parts business in Mpls, (Nat'l Impala Assoc.) had one on the shelf. This guy's dad started an auto repair business back in '56 and the son eventually followed in his dad's footsteps while also collecting obsolete GM parts from local dealerships from the time he was 14 yrs. old (he's now 49). Now, that's all he does is sell NOS and nice used parts. Merry Christmas to me!! cheers

by 77mali Fri Dec 13, 2013 3:43 pm

Post a few pics of that NOS part please!

That's too bad you couldn't get a hold of him. Small businesses like those can be tough. I hope he didn't close up shop though.

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